More and more organizations want to run their own communication again: public administrations, schools, companies with sensitive data. Their reasons differ. Some want to know where their data is. Some don't want to depend on the prices and terms of one vendor. Some have rules that require it.
The servers are rarely the problem. Open mail, calendar and file servers are mature, and a mailbox migration can be planned for a weekend. The problem is the desk. People lose their habits overnight, the helpdesk is flooded, and management starts asking whether this was a good idea.
Separate the client from the server
Mail is two things: a client and a server, connected by protocols. If the client speaks the protocols of Microsoft and the open standards, you can change one side at a time.
Lookout does that. It connects to Exchange through EWS, OWA and ActiveSync, and to Microsoft 365 through Graph. It also connects to JMAP, IMAP, CalDAV, CardDAV and WebDAV servers. And it looks like Outlook.
Step 1: Change the client
Roll out Mustang with the Lookout interface. Keep Exchange or Microsoft 365 for now. On the first day, people see the ribbon, the folders and the shortcuts they know. Their mail, calendars and shared folders are where they were.
Step 2: Change the server
Move the mailboxes to servers that you run or trust: Stalwart, Nextcloud, openDesk or any other server with open standards. Then change the accounts in Mustang. For people at the desk, the window stays the same. Only the server behind it is new.
Step 3, if you like: Change the look
The modern interface of Mustang is one setting away. Some people will try it out of curiosity, others never will. Both are fine.
Where you end up
- Your mail is on your servers and on the computers of your people. It doesn't pass through any service in between.
- The client is open source under the EUPL 1.2, the license of the European Commission. You can read, audit and build it.
- You can change the server again later without retraining anyone, because the client speaks open standards.
- The vendor is a European company, Beonex GmbH in Germany.
The Exchange and Microsoft 365 connectors are proprietary, because the protocols of Microsoft are. They are part of a paid plan of Mustang, and you need them only while you use the servers of Microsoft.